Transparent electroconductive films are used for applications such as electrodes for inorganic EL panels, liquid crystal displays and solar batteries; hot wave reflection films for window glass; and antistatic films. Among the transparent conductive films, an indium-tin oxide film comprising an indium oxide containing 2 to 20% by weight of tin oxide has many applications because of its high electroconductivity (that is, low electric resistivity) and superior translucency. The “indium-tin oxide” is hereinafter referred to as ITO.
However, the ITO has problems that (1) it is expensive, because it contains an expensive indium oxide in an amount of from 80 to 98% by weight, and (2) its transparency is not good, because it absorbs light ranging from visible rays having short wave lengths to ultraviolet rays.
In the production of inorganic EL panels, it is required to use a transparent electroconductive film, which does not decrease its electroconductivity even when heat-treated in air at a temperature exceeding 800° C. However, a transparent electroconductive film comprising the ITO, which is usually used for the production of inorganic EL panels, has a problem that it decreases its electroconductivity when heat-treated under such conditions.
As one of transparent electroconductive materials substitutable for the ITO, InSbO4 is proposed. Said InSbO4 has characteristics that (1) it is cheaper than the ITO, because a content of the expensive indium oxide is only a half of that of the ITO on a weight basis, and (2) its transparency is superior to the ITO, because it absorbs little light ranging from visible rays having short wave lengths to ultraviolet rays. However, an InSbO4-containing transparent electroconductive film has never been obtained. For example, JP-A 9-71419 discloses a process for producing an InSbO4-containing sintered object comprising the steps of (i) shaping a mixed powder of an indium oxide powder and an antimony oxide powder to obtain a shaped product, and (ii) sintering the shaped product: however, it discloses no InSbO4-containing transparent electroconductive film.